Conflict between the Electronic Factors and Structure-Directing Rules in the Intergrowth Structure of Ca₄Ag_2+<i>x</i>Ge_4–<i>x</i> with <i>x</i> = 1/2

Combined experimental and theoretical efforts to conceptually understand the structure directing forces in intergrowth structures have led to the discovery of the new ternary phase Ca₄Ag_2+<i>x</i>Ge_4<i>–x</i> (<i>x</i> = 0.5), obtained from high-temperature reaction of the elements. It crystallizes in a new structure type according to single-crystal diffraction methods: monoclinic space group <i>C</i>2/<i>m–i</i>¹⁰ with <i>a</i> = 10.7516(2) Å, <i>b</i> = 4.5475(1) Å, <i>c</i> = 18.7773(4) Å, β = 93.69(2)°, <i>V</i> = 916.17(3) ų, <i>Z</i> = 4. The compound corresponds to the <i>n</i> = 2 member of the homologous series Ca_2+<i>n</i>Ag_2+<i>x</i>Ge_{2+<i>n–x</i>}, that are built up by linear intergrowths of slabs cut from the CaGe (CrB-type) and the CaAg_1+<i>x</i>Ge_1<i>–x</i> (KHg₂ or TiNiSi-type) structures, and may be partitioned in Ag-rich and Ag-free domains. Instead of the predicted Zr₂CoSi₂-type (<i>C</i>2/<i>m–i</i>⁵), a simultaneous doubling of the size of the two building blocks is observed with the dimerization of the (Ge₂) pairs into Ag-substituted tetramers (Ag_<i>x</i>Ge_4<i>–x</i>) due to valence electron shortage. However, the Ag/Ge mixing at one atomic site with roughly one-to-one atomic ratio is therefore unexplained. The electronic band structure calculations and analysis of the chemical bonding provided evidence that the Ag/Ge mixing is rather the result of a direct conflict between the Zintl-Klemm concept and empirically established “structure-directing rules”. The implications of these findings for the poorly understood ordered staging structural interfaces, typically observed in secondary Li-ion batteries during charge/discharge process, are briefly discussed

Drastic Change of Magnetic Interactions and Hysteresis through Site-Preferential Ru/Ir Substitution in Sc₂FeRu_5–<i>x</i>Ir_<i>x</i>B₂

The quinary members of the complex boride series Sc₂FeRu_5–<i>x</i>Ir_<i>x</i>B₂ were synthesized by arc melting the elements and characterized by powder and single-crystal X-ray diffraction as well as metallographic and energy-dispersive X-ray analyses. The use of a 4d/5d mixture allows distinguishing these elements with X-ray diffraction methods, thus enabling the study of site preference and its influence on the magnetic properties.The magnetic measurements reveal several changes of magnetic ordering within the series: from antiferromagnetism (Sc₂FeRu₅B₂) to ferromagnetism (Sc₂FeRuIr₄B₂) and finally to metamagnetism (Sc₂FeIr₅B₂). Within the quinary series, the magnetic moments continuously increase with increasing amounts of Ir in one (8<i>j</i>) of two possible Wyckoff sites. The members with <i>x</i> = 2 and 3 represent the first hard magnetic borides of transition metals

A Stacking Faults-Containing Silicogermanate with 24-Ring Channels and Unbranched <i>Zweier</i> Silica Double Chains

A novel open-framework silicogermanate SU-JU-14 (Stockholm University-Jilin University-Number 14), |NH₃CH₂CH₂NH₃|₃[Ge_6.40Si_0.60O₁₅(OH)]₂[Ge_0.73Si_3.27O₈], was synthesized by using ethylenediamine as the structure-directing agent under solvothermal conditions. Single-crystal structure analysis reveals that the crystal structure of SU-JU-14 consists of extended 24-ring channels built from [(Ge,Si)₇O₁₂O_6/2(OH)]^3– [(Ge,Si)₇] clusters and unbranched <i>zweier</i> silica double chains [Ge_0.73Si_3.27O₄O_8/2]. Charge neutrality is achieved by diprotonated ethylenediamine guest molecules. The structure consists of stacking faults of layered arrays in two different configurations along the <i>a</i>-axis. SU-JU-14 was characterized by X-ray diffraction, X-ray energy dispersive spectroscopy, scanning electron microscopy, nuclear magnetic resonance, inductively coupled plasma, and thermogravimetric analyses. Crystallographic data: monoclinic, space group <i>C</i>2/<i>c</i>, and unit cell parameters: <i>a</i> = 35.625 (7) Å, <i>b</i> = 28.580 (6) Å, <i>c</i> = 10.403 (2) Å, and β = 98.30 (3)°

A Stacking Faults-Containing Silicogermanate with 24-Ring Channels and Unbranched <i>Zweier</i> Silica Double Chains

A novel open-framework silicogermanate SU-JU-14 (Stockholm University-Jilin University-Number 14), |NH₃CH₂CH₂NH₃|₃[Ge_6.40Si_0.60O₁₅(OH)]₂[Ge_0.73Si_3.27O₈], was synthesized by using ethylenediamine as the structure-directing agent under solvothermal conditions. Single-crystal structure analysis reveals that the crystal structure of SU-JU-14 consists of extended 24-ring channels built from [(Ge,Si)₇O₁₂O_6/2(OH)]^3– [(Ge,Si)₇] clusters and unbranched <i>zweier</i> silica double chains [Ge_0.73Si_3.27O₄O_8/2]. Charge neutrality is achieved by diprotonated ethylenediamine guest molecules. The structure consists of stacking faults of layered arrays in two different configurations along the <i>a</i>-axis. SU-JU-14 was characterized by X-ray diffraction, X-ray energy dispersive spectroscopy, scanning electron microscopy, nuclear magnetic resonance, inductively coupled plasma, and thermogravimetric analyses. Crystallographic data: monoclinic, space group <i>C</i>2/<i>c</i>, and unit cell parameters: <i>a</i> = 35.625 (7) Å, <i>b</i> = 28.580 (6) Å, <i>c</i> = 10.403 (2) Å, and β = 98.30 (3)°